Polyamide substrates, such as carpeting, upholstery fabric and the like, are subject to staining by a variety of agents, e.g., foods and beverages. An especially troublesome staining agent is FD&C Red Dye No. 40, commonly found in soft drink preparations. Different types of treatments have been proposed to deal with staining problems. One approach is to apply a highly fluorinated polymer to the substrate. Another is to use a composition containing a sulfonated phenol-formaldehyde condensation product.
For example, Liss and Beck, in U.S. patent application Ser. No. 124,866, filed Nov. 23, 1987, disclose stain-resistant synthetic polyamide textile substrates having modified sulfonated phenol-formaldehyde polymeric condensation products deposited on them.
Blyth and Ucci, in U.S. Pat. No. 4,592,940, describe the preparation of stain-resistant nylon carpet by immersing the carpet in an aqueous solution of a sulfonated condensation polymer wherein at least 40% of the polymer units contain --SO.sub.3 .times.radicals and at least 40% of the polymer units contain sulfone linkages. On the other hand, in U.S. Pat. No. 4,501,591, Ucci and Blyth disclose continuously dyeing polyamide carpet fibers in the presence of an alkali metal meta silicate and a sulfonated phenol-formaldehyde to the dyed carpet. They report that in experiments in which either the alkali meta silicate or condensation product was omitted from the dyeing process, or in which silicates other than the alkali metal meta silicates were used, they failed to obtain stain-resistant carpets (column 8, lines 4-12).
Frickenhaus et al., in U.S. Pat. No. 3,790,344, disclose a process for improving fastness to wet processing of dyeings of synthetic polyamide textile materials with anionic or cationic dye stuffs. After dyeing the textile materials, Frickenhaus et al. treated the dyed materials with condensation products prepared from 4,4'-dioxydiphenylsulphon, formaldehyde and either a phenol sulfonic acid, a naphthalene sulfonic acid, sodium sulfite or sodium hydrogen sulfite.
However, sulfonated phenol-formaldehyde condensation products are themselves subject to discoloration; commonly they turn yellow. Yellowing problems are described by W. H. Hemmpel in a Mar. 19, 1982 article in America's Textiles, entitled Reversible Yellowing Not Finisher's Fault. Hemmpel attributes yellowing to exposure of a phenol-based finish to nitrogen oxides and/or ultraviolet radiation. Critchley et al., Heat Resistant Polymers; Technologically Useful Materials, Plenum Press, N.Y. 1983, state that the thermo-oxidative stability of phenol-formaldehyde condensation products can be improved by etherifying or esterifying the phenolic hydroxyl groups.
To deal with the yellowing problem, Marshall, in application Ser. No. 173,324 filed Mar. 25, 1988, now U.S. Pat. No. 4,833,009, removes color-formers by dissolving the condensation product in aqueous base, acidifying the solution to form a slurry, heating the slurry so as to cause phase separation, recovering water-insoluble material and dissolving the water-insoluble material in aqueous base. On the other hand, Liss and Beck, in their aforesaid application, remove color-formers by acylating or etherifying a sufficient number of the free phenolic hydroxyls of the condensation product so as to inhibit yellowing of said condensation product but insufficient so as to reduce materially its capacity to impart stain resistance to a synthetic polyamide textile substrate. In a preferred embodiment, the acylated or etherified condensation product is dissolved in a hydroxy-containing solvent, such as ethylene) glycol, prior to its being applied to the textile substrate.
Orito et al., in Japanese Published Patent Application Topkukai 48-1214, describe preparing flame-retardant filaments by (a) reacting (i) a phenol-containing compound, (ii) benzoquanamine, melamine or a methylol derivative thereof and (iii) formaldehyde; (b) forming filaments by melt-spinning the resulting polymer and (c) reacting the filaments with an esterifying or etherifying agent so as to effect color change in the filaments. In an example, soaking the filaments in acetic anhydride for five days caused their color to change from pink to pale yellow.
Meister et al., in U.K. Patent Specification 1 291 784, disclose condensation products of 4,4'-dihydroxydiphenylsulphone, diarylether sulphonic acids and formaldehyde, and the use of such condensation products as tanning agents and as agents for improving the fastness to wet processing of dyeings obtained on synthetic polyamides with anionic and/or cationic dyestuffs. Meister et al. disclose that by preparing their condensation products in an acid pH range, leathers tanned with the condensation products showed practically no yellowing after 100 hours exposure to light in Xenotest apparatus.
Allen et al., in U.S. Pat. No. 3,835,071, disclose rug shampoo compositions which upon drying leave very brittle, non-tacky residues which are easily removed when dry. The compositions comprise water-soluble metal, ammonium or amine salt of a styrene-maleic anhydride copolymer, or its half ester, and a detergent. Water-soluble metal salts of Group II and the alkali metals (particularly magnesium and sodium) are preferred, and ammonium salts are most preferred by Allen et al.